The horizontal column location is critical for
correctly decoding the numbers. There are 7 items possible with the
first item listed directly below the first letter of the rear axle code,
or column number 15 and the column number is how they will be designated
below.

*Note: Several Fremont and Atlanta warranty cards have been seen with
the numbers "4" and/or "7" in the C-20 position. These codes are listed
in one reference, MSA-1 Chevy Cowl Tag Code Guide, but not in
other reference material found so far.